Re: [PATCHv2] mm: fix incorrect vbq reference in purge_fragmented_block

[hailong liu]

On Fri, 31. May 08:50, zhaoyang.huang wrote:
> From: Zhaoyang Huang <zhaoyang.huang@xxxxxxxxxx>
>
> vmalloc area runs out in our ARM64 system during an erofs test as
> vm_map_ram failed[1]. By following the debug log, we find that
> vm_map_ram()->vb_alloc() will allocate new vb->va which corresponding
> to 4MB vmalloc area as list_for_each_entry_rcu returns immediately
> when vbq->free->next points to vbq->free. That is to say, 65536 times
> of page fault after the list's broken will run out of the whole
> vmalloc area. This should be introduced by one vbq->free->next point to
> vbq->free which makes list_for_each_entry_rcu can not iterate the list
> and find the BUG.
>
> [1]
> PID: 1        TASK: ffffff80802b4e00  CPU: 6    COMMAND: "init"
>  #0 [ffffffc08006afe0] __switch_to at ffffffc08111d5cc
>  #1 [ffffffc08006b040] __schedule at ffffffc08111dde0
>  #2 [ffffffc08006b0a0] schedule at ffffffc08111e294
>  #3 [ffffffc08006b0d0] schedule_preempt_disabled at ffffffc08111e3f0
>  #4 [ffffffc08006b140] __mutex_lock at ffffffc08112068c
>  #5 [ffffffc08006b180] __mutex_lock_slowpath at ffffffc08111f8f8
>  #6 [ffffffc08006b1a0] mutex_lock at ffffffc08111f834
>  #7 [ffffffc08006b1d0] reclaim_and_purge_vmap_areas at ffffffc0803ebc3c
>  #8 [ffffffc08006b290] alloc_vmap_area at ffffffc0803e83fc
>  #9 [ffffffc08006b300] vm_map_ram at ffffffc0803e78c0
>
> Fixes: fc1e0d980037 ("mm/vmalloc: prevent stale TLBs in fully utilized blocks")
>
> Signed-off-by: Zhaoyang Huang <zhaoyang.huang@xxxxxxxxxx>
> ---
> v2: introduce cpu in vmap_block to record the right CPU number
> ---
> ---
>  mm/vmalloc.c | 11 +++++++----
>  1 file changed, 7 insertions(+), 4 deletions(-)
>
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index 22aa63f4ef63..ca962b554fa0 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -2458,6 +2458,7 @@ struct vmap_block {
>  	struct list_head free_list;
>  	struct rcu_head rcu_head;
>  	struct list_head purge;
> +	unsigned int cpu;
>  };
>
>  /* Queue of free and dirty vmap blocks, for allocation and flushing purposes */
> @@ -2574,6 +2575,7 @@ static void *new_vmap_block(unsigned int order, gfp_t gfp_mask)
>  	vb->dirty = 0;
>  	vb->dirty_min = VMAP_BBMAP_BITS;
>  	vb->dirty_max = 0;
if task migration to other CPU at this time, this may lead to get incorrect vbq.
> +	vb->cpu = smp_processor_id();
>  	bitmap_set(vb->used_map, 0, (1UL << order));
>  	INIT_LIST_HEAD(&vb->free_list);
>
> @@ -2614,9 +2616,10 @@ static void free_vmap_block(struct vmap_block *vb)
>  }
>
>  static bool purge_fragmented_block(struct vmap_block *vb,
> -		struct vmap_block_queue *vbq, struct list_head *purge_list,
> -		bool force_purge)
> +		struct list_head *purge_list, bool force_purge)
>  {
> +	struct vmap_block_queue *vbq = &per_cpu(vmap_block_queue, vb->cpu);
> +
>  	if (vb->free + vb->dirty != VMAP_BBMAP_BITS ||
>  	    vb->dirty == VMAP_BBMAP_BITS)
>  		return false;
> @@ -2664,7 +2667,7 @@ static void purge_fragmented_blocks(int cpu)
>  			continue;
>
>  		spin_lock(&vb->lock);
> -		purge_fragmented_block(vb, vbq, &purge, true);
> +		purge_fragmented_block(vb, &purge, true);
>  		spin_unlock(&vb->lock);
>  	}
>  	rcu_read_unlock();
> @@ -2801,7 +2804,7 @@ static void _vm_unmap_aliases(unsigned long start, unsigned long end, int flush)
>  			 * not purgeable, check whether there is dirty
>  			 * space to be flushed.
>  			 */
> -			if (!purge_fragmented_block(vb, vbq, &purge_list, false) &&
> +			if (!purge_fragmented_block(vb, &purge_list, false) &&
>  			    vb->dirty_max && vb->dirty != VMAP_BBMAP_BITS) {
>  				unsigned long va_start = vb->va->va_start;
>  				unsigned long s, e;
> --
> 2.25.1
>
>

--

Best Regards,
Hailong.